Why modern felt roofing still remains one of the best waterproofing options

Roofing specifications often distinguish between SBS and APP modified bitumen, but the real story lies in how today’s formulations perform over the long term. While SBS has traditionally been associated with enhanced flexibility, advances in APP technology mean that high-quality products with this formulation, now accommodate structural movement far more effectively than earlier generations. 

These improved plastomeric blends remain stable across the temperature swings typical of the UK climate, resisting softening under high summer heat and maintaining integrity under foot traffic, which helps reduce mechanical damage. APP capsheets also offer strong UV resistance without additional protection and have proved more resilient against challenges such as bird fouling and surface attack. The result is that modern APP systems deliver a level of stability, durability and movement tolerance that gives contractors confidence across both new and existing roofs, ensuring reliable, predictable performance over decades.

Refurbishment contractors also know that few roofs offer the clean, uniform conditions seen in new-build projects. Uneven substrates, historical movement and variable surfaces all demand a membrane that can adapt rather than fail under stress. Modern two-layer felt systems are designed precisely for this environment. The reinforced underlay accommodates structural movement and irregularities in the deck, while the bonded cap sheet provides a robust, high-resilience surface with strong puncture and impact resistance. Together, the layers work as a unified system that tolerates imperfections, maintains adhesion and delivers reliable waterproofing even on roofs that present challenges no single-layer product could manage alone. 

Full adhesion, whether torch-applied or self-adhesive, creates a monolithic system that resists wind uplift and avoids the fluttering, membrane “drumming” or fastener stress concentrations associated with mechanically-fixed systems. On roofs with variable substrate conditions, bituminous membranes are simply more forgiving.
In refurbishment projects, trapped moisture within the existing roof build-up can present a real risk, particularly when heat causes that moisture to turn to vapour. While bituminous felts themselves are not breathable, modern systems offer practical ways to manage this challenge without compromising long-term performance. A vented base layer can be introduced when overlaying an existing roof, creating pathways that allow vapour to disperse safely rather than build up beneath the membrane. This approach gives contractors a controlled method for dealing with entrapped moisture while still delivering a stable, fully bonded waterproofing system.

The real numbers behind long-term performance
While published life expectancies vary, experienced contractors know that a well-designed and properly installed built-up bituminous system consistently delivers in excess of 30 years of service. That longevity is not theoretical - it has been observed across thousands of UK roofs dating back to the early modified-bitumen era. When failures occur, they almost always relate to workmanship or detailing, not membrane breakdown. This is a key reason felt systems retain such a strong track record in public-sector estates, schools and social housing portfolios.
As an example, the Proteus Pro-Felt® Ultima Plus system represents the latest generation of APP-modified torch-on membranes, designed for durability, dimensional stability and long-term performance. BBA certified with a service life in excess of 30 years, Ultima Plus is suitable for both new-build and refurbishment projects, offering a flexible solution for warm roof assemblies or as a standalone overlay. Its mineral capsheet, combined with single-strand composite polyester reinforcement and a choice of sanded or self-adhesive underlays, creates a robust multi-layer system that delivers consistent mechanical strength, resistance to thermal movement and reliable waterproofing in demanding applications, including roofs with limited access.
The system works particularly well with thicker insulation layers, tapered schemes and hybrid warm-roof/cold-roof scenarios, which have become increasingly common due to regulatory changes. Such installations have changed how membranes move and where stresses accumulate. 

Why bitumen systems offer greater diagnostic control
Experienced roofers have seen the typical causes of premature failure, such as poor upstand details, insufficient laps, inadequate bonding at perimeters or outlets, or ponding caused by poor falls. These issues affect all membranes, but bituminous systems provide two key advantages - failures are rarely catastrophic because they start small and remain localised and any defects are easier to identify and rectify.
The layered nature of felt also means many roofs can be renewed or upgraded without removing the entire system, preserving budgets and minimising disruption on live buildings.
However, roofing professionals understand that a membrane is only as good as the team installing it. Bituminous systems offer a level of installation control that alternative membranes don’t always match. Torch-applied systems provide immediate visual confirmation of bonding, while cold-applied and self-adhesive systems reduce fire risk while still delivering uniform adhesion.Unlike some single-ply systems, bituminous membranes are not highly sensitive to solvent flash-off rates, humidity windows or narrow welding tolerances. This helps ensure that a competent installer can deliver predictable results across a wide range of site conditions.

Where felt still outperforms “newer” membrane systems
Despite shifting market trends, felt remains the most reliable choice in several critical situations. It is particularly effective on roofs subject to regular foot traffic, such as plant rooms and maintenance routes, thanks to its high puncture resistance. Felt also performs exceptionally well on refurbishment projects with unknown or uneven substrates, where its movement tolerance and adhesive flexibility can accommodate structural irregularities. 
Additionally, it is ideal for roofs that require staged installation, allowing phased works without compromising the waterproofing integrity. On sites where long-term repairability is a priority, such as housing association properties, council buildings and commercial estates, felt offers a practical and durable solution. For many contractors, these conditions are not exceptional cases, but represent the majority of real-life roofing projects.
Equally as important, bituminous roofs respond extremely well to routine maintenance. Clearing outlets, checking laps and addressing localised wear extends their life significantly. Because repairs can be integrated easily, facility managers often avoid the “all-or-nothing” refurb decisions that come with other membrane types. This maintains asset value and spreads expenditure more predictably.
So, despite new products entering the market, modern felt roofing remains one of the most robust, adaptable and installer-friendly waterproofing systems available. Its predictable behaviour, tolerance of imperfect substrates, excellent repairability and proven long-term performance continue to make it a practical and commercially sound choice for roofing professionals.